The Upgraded Falcon 9 vehicle for the first Iridium NEXT mission is prepared for launch. Photo Credit: SpaceX/Matt Desch/Twitter

Four months after an Upgraded Falcon 9 booster catastrophically exploded on Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla.—destroying both the vehicle and its payload, the Amos-6 communications satellite—SpaceX is ready for its second Return-to-Flight (RTF) in just over a year. The Hawthorne, Calif.-headquartered launch services organization plans to launch 10 Iridium NEXT global mobile telecommunications satellites into low-Earth orbit, no sooner than 9:54 a.m. PST Saturday, 14 January. The mission will be SpaceX’s third launch from Space Launch Complex (SLC)-4E at Vandenberg Air Force Base, Calif.

Originally targeted for launch on Sunday, 8 January, the customary Static Fire Test was performed successfully on Thursday. “Hold-down firing of @SpaceX Falcon 9 at Vandenberg Air Force Base completed,” tweeted SpaceX CEO Elon Musk on Thursday afternoon. “All systems are Go for launch next week.” However, with the Amos-6 investigation still awaiting official closure from the Federal Aviation Administration (FAA)—which carries executive oversight and responsibility for issuing the customary launch licenses—it remained to be seen if the target date would be met. However, on Friday morning, the FAA announced that it was satisfied with the Amos-6 investigation report and issued the requisite licenses, allowing work to progress toward an opening launch attempt on Monday. “The FAA accepted the investigation report on the AMOS-6 mishap and has closed the investigation,” it was noted. “SpaceX applied for a license to launch the Iridium NEXT satellites from Vandenberg Air Force Base. The FAA has granted a license for that purpose.” It was stressed that the conditions included a landing of the Upgraded Falcon 9 hardware either in the ocean or on the Autonomous Spaceport Drone Ship (ASDS).

Unfortunately, Mother Nature had other ideas, with high winds and rain forecast for Vandenberg throughout most of this week. “Launch moving due to high winds and rains at Vandenberg,” SpaceX tweeted on Sunday morning. “Other range conflicts this week results in next available launch date being Jan 14.”

In spite of the assurances from SpaceX and Iridium that Saturday was the formal target, it was not until Friday afternoon that the 30th Space Wing at Vandenberg confirmed Western Range readiness to support the launch. It was noted that the final FAA conditions were removed at 12:39 p.m. PST, allowing for authorization to proceed. “Vandenberg looks forward to the inaugural launch of Iridium NEXT and the return to flight of SpaceX,” said Col. J. Christopher Moss, 30th Space Wing Commander, who will be the Launch Decision Authority for tomorrow’s launch attempt. “This is an exciting mission and we have worked closely with our mission partners at SpaceX to ensure a safe and successful launch.” SpaceX also highlighted a 60-percent likelihood of acceptable weather conditions for launch.

Saturday’s flight is the first of seven launches for which SpaceX is contracted to transport 70 Iridium NEXT satellites into orbit. When the details for this mammoth contract were agreed between SpaceX and Iridium, back in June 2010, it marked the largest single launch deal ever signed, worth some $492 million. Over the coming months and years, Iridium NEXT will completely replace an aging network of first-generation Iridium satellites, whose earliest members were launched two decades ago.

In fact, from May 1997 until June 2002, a total of 95 first-generation Iridium satellites were inserted into low-Earth orbit, via four different vehicles and from four different locations: aboard Delta II rockets from Vandenberg Air Force Base, Calif., aboard Proton-K and Rokot-KM boosters from Russia’s Baikonur and Plesetsk cosmodromes and aboard the workhorse Cheng Zheng (CZ)-2C from the Taiyuan Satellite Launch Center in China’s northern Shanxi Province. Developed and owned by Motorola, the first-generation Iridiums were built by Lockheed Martin on the basis of its LM-700 “bus,” with each satellite weighing around 1,520 pounds (690 kg) and deriving electrical power from a pair of deployable solar arrays and associated batteries.

The Iridium NEXT satellites are encapsulated into the Upgraded Falcon 9 payload fairing last month. Photo Credit: SpaceX/Iridium

Iridium was intended as a global mobile telecommunications network, employing dozens of small satellites in low-Earth orbit. By routing signals via Ka-band from satellite to satellite, using on-board processing, it was expected that the problems of weak reception at higher latitudes from geostationary satellites could be overcome. “Anyone with an Iridium phone would be within sight of a satellite,” noted New Scientist in a recent article, “and those satellites would communicate with each other, enabling everyone on Earth to talk to everyone else.” Original plans called for a total of 77 Iridiums to be launched—hence the name, which honored the metal with atomic number 77—but it was eventually concluded that just 66 were required. Additionally, Iridium carries a number of on-orbit spares.

The satellites occupy high-inclination, near-polar orbits of 86.4 degrees and operate at an altitude of approximately 485 miles (780 km). The first Iridium telephone call was made by then-U.S. Vice President Al Gore in November 1998, who used a handset in the White House Rose Garden to call National Geographic Society Chairman Gilbert Grosvenor, great-grandson of Alexander Graham Bell.

However, by the time it entered operational service, the Iridium concept was already obsolete and its market success was not strong; by the turn of the millennium it had gone bankrupt. Yet it endured as a means of covering regions of Earth where reliable geosynchronous communications was sparse or non-existent and its users included explorers and the military. As of today, some 64 of the 66 Iridium satellites needed for “seamless” global coverage are operational.

Planning for the next generation, dubbed “Iridium NEXT,” was announced in early June 2010, and Thales Alenia Space and its subcontractor Orbital Sciences Corp. (later Orbital ATK) was selected to build 66 operational satellites and six on-orbit and nine ground-based spares, at an anticipated cost of $2.9 billion. Iridium NEXT would be based upon the Extended LifeTime Bus (ELiTeBus)-1000 design, previously employed for the low-Earth-orbiting GlobalStar communications satellites, launched between 2006 and 2012. Weighing 1,760 pounds (800 kg), the Iridium NEXT satellites would be powered by twin solar arrays and would operate at an altitude of 485 miles (780 km), inclined 86.4 degrees to the equator and capable of supporting a decade-long lifespan. The solar arrays—spanning 31 feet (9.4 meters) when fully unfurled and capable of generating 2 kilowatts—would offer a 50-percent uplift over the power-producing potential of the original Iridium satellites.

Also in June 2010, SpaceX was selected to deliver the Iridium NEXT constellation in its entirety to orbit, with seven launches out of Vandenberg Air Force Base between 2015 and 2017. “The $492 million contract,” explained Iridium in a news release, “while being the largest single commercial launch deal ever signed, nonetheless represents a new benchmark in cost-effective satellite delivery to space.”

Moscow-based International Space Company (ISC) Kosmotras was also contracted in June 2011 as a “supplemental provider of launch services,” with the expectation that its silo-launched Dnepr booster would deliver the first two Iridium NEXT satellites to orbit in April 2016, with SpaceX’s launches expected to begin later that summer. However, according to Space News, Iridium became frustrated by Russian red tape—specifically delays in the issuance of licenses by the Russian Ministry of Defense—and the Dnepr launch will now likely occur further downstream.

The Amos-6 accident on 1 September 2016. Photo Credit: www.USLaunchReport.com

The expectation was that the entire Iridium NEXT constellation would be delivered to orbit before the end of 2017. Unfortunately, last September’s explosion of an Upgraded Falcon 9 booster on Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla.—which destroyed both the vehicle and its payload, the Amos-6 communications satellite—grounded the SpaceX fleet, as investigators sought the cause of the accident. Early in December, Iridium announced a revised target date of No Earlier Than (NET) 16 December, with an Upgraded Falcon 9 boosting 10 Iridium NEXT satellites into orbit from Space Launch Complex (SLC)-4E at Vandenberg. On 8 November, Mr. Desch tweeted his 1,850 followers that the second stage of the Upgraded Falcon 9 for Iridium NEXT’s first mission had arrived safely at Vandenberg. Less than two weeks later, on the 20th, he added that the first stage hardware had also arrived.

However, as noted by AmericaSpace’s Mike Killian in a recent article, the launch slipped into January 2017 as SpaceX sought “to complete the final steps necessary to safely and reliably return to flight.” The news of the delay was disappointing, though unsurprising, in view of the still-unclosed nature of the Amos-6 investigation. “Santa delaying my Xmas present, but agree with @SpaceX on the new plan,” tweeted Mr. Desch on 16 December. “Few weeks delay—exciting start to 2017!” He subsequently shared images of the Upgraded Falcon 9 undergoing final processing and, by Christmas week, the 10 fully fueled Iridium NEXT satellites were stacked in their dispenser for emplacement aboard the booster. In keeping with new procedures, implemented since the Amos-6 explosion, SpaceX will now install payloads aboard the booster after the Static Fire Test. With the completion of the test on Thursday, the Iridium NEXT payload was loaded over the weekend.

In its 28 flights completed to date, the Falcon 9 has delivered 15 major payloads to low-Earth orbit—including nine Dragon cargo ships, bound for the International Space Station (ISS)—together with 11 communications satellites to geosynchronous orbit and a handful of scientific spacecraft to other locations, including near-polar orbit and further afield to the Sun-Earth L1 Lagrangian Point. The Falcon 9 suffered a major failure during flight on 28 June 2015, destroying its Dragon payload, and endured another serious accident on 1 September 2016, when it catastrophically exploded on the launch pad.